Differences in pulmonary function measured by oscillometry between horses with mild-moderate equine asthma and healthy controls.

BACKGROUND

The diagnosis of mild-moderate equine asthma (MEA) can be confirmed by airway endoscopy, bronchoalveolar lavage fluid (BALf) cytology, and lung function evaluation by indirect pleural pressure measurement. Oscillometry is a promising pulmonary function test method, but its ability to detect subclinical airway obstruction has been questioned.

OBJECTIVES

To evaluate the differences in lung function measured by oscillometry between healthy and MEA-affected horses.

STUDY DESIGN

Prospective case-control clinical study.

METHODS

Thirty-seven horses were divided into healthy and MEA groups, based on history and clinical score; the diagnosis of MEA was confirmed by airway endoscopy and BALf cytology. Horses underwent oscillometry at frequencies ranging from 2 to 6 Hz. Obtained parameters included whole-breath, inspiratory, expiratory, and the difference between inspiratory and expiratory resistance (Rrs) and reactance (Xrs). Differences between oscillometry parameters at different frequencies were evaluated within and between groups by repeated-measures two-way ANOVA and post hoc tests with Bonferroni correction. Frequency dependence was compared between groups by t test. For significant parameters, a receiver operating characteristics curve was designed, cut-off values were identified and their sensitivity and specificity were calculated. Statistical significance was set at p < 0.05.

RESULTS

No significant differences in Xrs and Rrs were observed between groups. The frequency dependence of whole-breath and inspiratory Xrs significantly differed between healthy (respectively, -0.03 ± 0.02 and -0.05 ± 0.02 cmHO/L/s) and MEA (-0.1 ± 0.03 and -0.2 ± 0.02 cmHO/L/s) groups (p < 0.05 and p < 0.01). For inspiratory Xrs frequency dependence, a cut-off value of -0.06 cmHO/L/s was identified, with 86.4% (95% CI: 66.7%-95.3%) sensitivity and 66.7% (95% CI: 41.7%-84.8%) specificity.

MAIN LIMITATIONS

Sample size, no BALf cytology in some healthy horses.

CONCLUSIONS

Oscillometry can represent a useful non-invasive tool for the diagnosis of MEA. Specifically, the evaluation of the frequency dependence of Xrs may be of special interest.